Page:Popular Science Monthly Volume 17.djvu/32

22 of the tasimeter, what was previously only a matter of conjecture was proved to be a certainty—that the corona of the sun emits heat. The apparatus above described was arranged with as much care as possible, so that the smallest amount of heat might be detected. So great was the delicacy of the instrument that, at the time of total eclipse, when the beam from the corona was allowed to fall upon the tasimeter, the spot of light reflected from the galvanometer mirror not only changed its position, but moved completely off the scale which had been provided; so that, while the presence of heat in the corona was demonstrated, measurement of it was impossible. The instrument has also been used in measuring the heat of some of the stars.



Besides being used as a delicate thermometer, the tasimeter also serves as a means of determining the coefficient of expansion of bodies; for, by having a micrometer screw attachment, the amount of expansion can be readily determined. By turning the screw, when the needle has been deflected, until it is brought back to zero, the increase in length can be read by the number of turns or parts of a turn the screw has been moved. Fig. 8 gives a section of the tasimeter, showing the micrometer screw. The piece of material to be tested is seen at A, being clamped rigidly at B, and resting in a metal socket M, which rests upon the carbon placed in the battery circuit as indicated.